This invention relates to liquid fuel campstoves, and, more particularly, to liquid fuel campstoves with a piezoelectric electronic ignition system.
Conventional liquid fuled stoves are match lit. This requires the customer to strike a match and hold it near the stove's main burner and then to properly set the stove fuel control valve for the ignition cycle. This is inconvenient, and the difficulty of getting everything done quickly and in the right order, particularly in wet and windy conditions, can result in an excessive amount of unvaporized fuel collecting in the lower part of the stove's burner venturi area. The excess fuel condition is called flooding and results in a lazy yellow-colored flame which extends a few inches above the burner. This flame gradually subsides as the excess fuel is depleted and the generator gets hot.
In a conventional liquid fueled stove such as the ones which Coleman has offered for many years, fuel is contained in a pressure vessel into which air is pumped under pressure. See, for example, U.S. Pat. No. Re. 29,457. The vessel is equipped with a dip tube which extends to nearly the bottom of the tank. The dip tube is closed at the bottom with the exception of a small diameter orifice through which fuel is allowed to enter. The dip tube has an internal conduit which is open at the bottom and which communicates with the upper part of the pressure vessel above the maximum intended fuel level. The dip tube orifice can be partly blocked by insertion of a needle which is suitably connected to the fuel control system so as to cause it to partly block the orifice during the lighting cycle and to leave the orifice unblocked during the normal burn cycle. The upper end of the dip tube is connected through a valve system to a generator. The generator is a metal tube which passes above the burner of the stove into a venturi assembly which is connected to a burner. Fuel is discharged at high velocity from an orifice at the end of the generator into the venturi where air is aspirated and mixed and fed to the burner as a combustible mixture for burning. During the lighting cycle, unvaporized gasoline is discharged through the orifice and is not readily ignitable. To overcome this problem, the dip tube needle is used to partly block the fuel entry orifice. This creates a pressure imbalance within the dip tube which permits pressurized air to flow through the passageway inside of the dip tube from above the fuel. This pressurized air mixes with the liquid fuel and moves with it to be discharged from the generator orifice. The air fuel mixture at discharge consists of fuel-vapor-laden air and atomized droplets of fuel which can be readily ignited.
In the conventional arrangement, the pressure vessel is an elongated cylinder which is hung in a horizontal orientation on the outside of a case which contains the venturi and burner assemblies. The venturi is U-shaped, and the generator discharge orifice is inserted in one of the legs of the "U". The burner is attached at a 90.degree. angle to the end of the other leg of the "U". In this configuration, the mixture of fuel vapor-laden air and atomized droplets of fuel must make a 180.degree. turn and a 90.degree. turn before finally reaching the burner for combustion. Under start up, the venturi parts are cold and contact between the mixture and the cold metal causes much of the liquid fuel to drop out. This in turn causes the fuel air mixture at the burner to be at the low end of the range of combustibility (lean) and difficult to light. This condition becomes more severe at lower ambient temperatures.
Campstoves and lanterns have been provided which include a piezoelectric ignition device. For example, U.S. Pat. Nos. 4,691,136 and 4,870,314 describe lanterns with a piezoelectric ignitor. Coleman has also offered propane fueled campstoves with piezoelectric ignition.
In a liquid fuel campstove the air fuel mixture at the burner becomes too lean to be ignited by a piezoelectric ignitor once ambient temperature falls to about 40.degree. F. Match lighting of the appliance also becomes increasingly difficult, and the appliance is prone to flooding prone below this temperature.